The present invention generally relates to artificial lift systems which are utilized for production of fluids from subsurface reservoirs, including oil, water, and liquid phase hydrocarbons. More particularly, the present invention is utilized with artificial lift systems where a subsurface pump is actuated by a plurality of rods connected end-to-end, herein collectively referred to as a “rod string.” The rod string is set within a plurality of tubing joints likewise connected end-to-end, wherein the tubing joints are collectively referred to as a “tubing string.” Actuation of the subsurface pump lifts the fluid upwardly from the subsurface pump to the surface, where the fluids flow in the annular space between the rod string and the inside diameter of the tubing string as the fluid flows upwardly.
The typical subsurface pump operated by a rod string is a positive displacement pump operated by reciprocation of the rod string. This type of pump has a plunger connected to the rod string, where the plunger reciprocates within a polished barrel located at the bottom of the tubing string such that liquids are drawn into the pump barrel and lifted upwardly through the tubing string. The reciprocating motion of the rod string is typically imparted by a pump jack.
For this system, the uppermost rod in the rod string is a polish rod. The polish rod reciprocates in and out of a stuffing box. The stuffing box is a close-fit assembly which cleans the polished rod, prevents debris from entering or exiting the well, and further prevents fluid from leaking from the well during operation. The stuffing box is typically mounted above a T-fitting or pumping tee cross at the top of the tubing. The stuffing box provides a dynamic seal along the length of the polish rod. The stuffing box typically has a central passage through which the polish rod moves, while stuffing or packing material is compressed against the sides of the polish rod to create a fluid seal. The packing materials are typically elastomers and other materials which are softer than the polish rod material.
The movement of the polish rod within the packing material generates friction, and thus heat, which breaks down and degrades the packing materials contained within the stuffing box. This breakdown and degradation reduces the integrity of the seal formed between the packing material and the polish rod. The presence of solids in the produced fluid, such as sand, can accelerate this degrading of the packing material and can adversely impact the life of the polish rod, potentially resulting in a polish rod failure. The loss of the integrity of the seal between the polish rod and the packing material will result in the escape of fluids from the well which can result in environmental damage and the loss of valuable resources, and can result in significant clean-up expense and potential fines and penalties. Accelerated packing replacement also requires the expenditure of man-hours to replace the packing which might otherwise be avoided.
Solutions to the above problem typically focus on the packing material, such as utilizing a different type of packing material or attempting to reduce the friction between the polish rod and the packing material, and therefore reduce the thermal degradation.